Generator polarity control



May 23, 1950 Filed July 51, 1948 N BY Honsiuehl ATTORP} Y y 1950 R. SHOTTENFELD ET AL 2,508,727

GENERATOR POLARITY CONTROL 3 Sheets-Sheet 3 Filed July 31, 1948 I. mm W S N T R INVENTORS: Richard Shoflenfeld Hunsfifuehl Q r I HQ Q 3M2". E

ATTOR Y Patented May 23, 1950 UNITED STATES PATENT OFFICE GENERATOR POLARITY CONTROL Richard Shottenfeld, J amaica,.and Hans Kuehl, Hollis, N. Y

Application July 31, 1948, SerialNo. 41,847

7 Claims. 1

This invention relates to electroplating whereby the work being plated is subjected to plating with metal being electrolytically deposited on the workfrom a. metal-bearing solution or bath, the Work being one of two electrodes of the platingcurrent passing through the bath.

A mode of plating to which this invention relates consists of sending the plating current through the bath-for aninterval of time to efiect plating deposition of the metal, and then reversingthe direction of the current through the bath for a shorterinterval as compared with the; plating period in order to reverse the plating process during such shorter period. In. this way; plating periods, may alternate with deplating periodsrepeatedly adesirednumber of times, that is until certain requirements as to the thicknessof the deposit and as to quality of the surface finish of the plated Work are satisfied.

This mode of'plating operation poses a problem-because of difficultiesencountered in reversing the plating current, especially where the amperage of the current is high, as it may be on theorder of, several thousand amperes. Such high amperage plating current is usually supplied by a low-voltage high-current motor-driven enerator herein called the plating-generator. sucha generator usually. has itsfield windings energized or excited by a small auxiliary generator driven together. with .the plating-generator. The auxiliary-generator is briefly termed and usually known as. the exciter. The field windingsaretermedthefield,while an energizing current passing through-the field windings. is called the field current, and the voltage of such a current is called the field voltage.

A mode of reversing the current passing through the plating bath is to reversethe direction of the field current.

The field currentmay be reversedby operating a. reversing switch interposed between the output terminals of the exciter and the field terminals oi'the plating-generator. By the operation of such a switch the field terminals are disconnected from the exciter. output terminals and then re-connected in reverse polarity.v This operation interrupts the field current and then reestablishes it in reverse direction. The interruption of the field current is accompanied by arcing at the switch contacts, this being a welllgnown phenomenon and is objectionable because of its; destructive efiects upon the switch cQntacts.

Another well-known but. objectionable, phenomenon incident to theinterruption of the field current is a sudden. rise of the field voltage which may lead to. the damaging or destruction of the field windings.

Still another undesirable phenomenon accompanies the reversal of the field current of the plating-generator, and that is the slow rate at which the field re-builds after it has been re-connected reverse polarity to the exciter by the operation of the reversing switch. This reduces the efiiciency oi the plating operation because of the time required for the plating or de-plating current output of the plating-generator to become fully effective after each reversal, and because of the length of the inactive or dead period of the plating bath thus intervening between the platingand the deplating phase.

The plating operation may be said to consistof at least one operating cycle which comprises a plating phase, a deplating phase, and a pair of transition phases during which take place respectively the change from the deplatingto the plating phase an back from the platingto the deplating phase.

It is among the objects of this invention to efiect a rapid, smooth, and efficient reversal of the plating-current by the reversal of the polarity of the field of the plating-generator, and to do so by means of a reversing switch, yet without arcing, Without endangering the field windings of the plating generator, and with a minimum of time required for the re-building of the field.

According to this invention these ill effects are eliminated by the provision. and functioning of a resonant circuit which, while avoiding the arcing as well as undue voltage rise is also instrumental to minimizing the length of the transition period. That is to say, in order to effect a smooth as well as rapid reversal of the generator outputcurrent supplied to the plating bath this invention provides a resonant discharge circuit for the generator field, through which circuit the stored energy of the field discharges in the form of a. resonant wave or wavelike curve when the field-exciting current is interrupted. The wave is. a graph representing the resonant current as a function of time and linetuating about the abscissa of the graph so. that the points of intersection of the Wave with the abscissa represent zero values ofv the current. ihe portions or peaks of. the: wave above the abscissa represent values which are. opposite to the values representedby the. wave portions or valleys or inverted peaks which lie below the abscissa. In other words, the direction of the current represented by a peak above the abscissa is opposite to the direction of the current represented by the next following valley.

A resonant circuit comprises inductance as Well as capacitance, and it is called a parallel resonant circuit when inductance and capacitance are connected in parallel. As exemplified by the embodiment herein shown the invention employs a parallel resonant circuit.

After interruption of the field-exciting current at the end of a plating phase, this invention proposes to re-establish the current in reverse direction when the current of the resonant discharge herein termed the resonant current attains a value which encourages the re-establishment of the field-exciting current. For example, such a value is encountered when the resonant circuit attains a direction coinciding with said reverse direction of the field-exciting current, and more specifically when the resonant current attains the value of the first peak of the wave at which the direction of the resonant current not only coincides with the reverse direction of the fieldexciting current but also approximates the magnitude of that current.

In this way the generator output current for the plating bath is re-established in a direction opposite to its direction at the time of its interruption, for initiating a de-plating phase following a plating phase.

According to this invention the parallel resonant circuit comprises the field windings of the plating-generator as the inductance and a capacitance of suitable value connected in parallel with that inductance.

While the aforementioned reversing switch is in either one of its closed positions, the capacitance in parallel with the field has no effect. However, at the instant of opening of the switch, that is when either the platingor the deplating phase ends, the field current begins to fluctuate according to the law of a damped cosine wave while the field voltage begins to fluctuate according to a damped sine wave. If that fluctuation were permitted to continue on its natural course it would do so according to what is known as a damped cosine or sine wave respectively in the course of which the energy of the field would be exhausted. In other words, such damped waves are expressive of the manner in which the stored energy of the field is dissipated.

According to this invention this damped wave starting with the opening of the switch contacts is allowed to develop only partially, namely only to substantially the instant where the fluctuating current reaches the first peak value of opposite direction. Thus the field current has reversed its direction automatically and the field is now energized in the desired polarity and substantially to the extent desired. According to one embodiment of this invention the operation of the reversal switch is so timed as to close in reverse polarity substantially at the instant When the reverse current peak occurs. In this way the exciter (auxiliary generator) being reconnected to the field of the plating-generator finds that field substantially fully energized in the desired (reversed) direction. Thus during the timed transition phase between opening and closing in reverse polarity of the switch, there will have been effected an automatic reversal of the field current without arcing, and in a smooth, rapid, and efficient manner.

According to a practical embodiment the reversing switch is automatically actuated by a timing device to operate in repetitive cycles whereby a sequence of alternating platingand deplating phases of predetermined length are established.

Fig. 1 is a diagrammatic View showing the reversal switch in a position corresponding to the plating phase, the plating generator showing a corresponding polarity.

Fig. 1a is a detail view showing a timing member that controls the phases of the operating cycle.

Fig. 2 is a diagrammatic view showing the reversal switch in a position corresponding to the deplating phase, the plating-generator having the opposite polarity to that of Fig. 1.

Fig. 3 is a diagram showing how the plating generator field voltage and current vary during the plating-, transitional-, and deplating phases of the plating cycle.

Figs. 4 to 10 are symbolic views to indicate the progressive positions of a timer which governs the reversing-cycle, as coordinated to the Fig. 3 diagram.

Fig. 11 is a diagram showing a sequence of the Fig. 3 cycles.

Fig. 12 is an enlargement of the transitional phase 0 of the Fig. 3 field current diagram.

Figs. 13 to 15 show operating positions of the reversal switch as coordinated to the Fig. 12 transitional phase of the field current.

Figs. 16, 17, 18 show in terms of wiring diagram the connections made by the reversal switch positions of Figs. 13, 14:, 15 respectively.

According to the wiring diagrams of Figs. 1 and 2, the system comprises a plating tank ll containing the plating solution or bath IS in which are immersed a pair of electrodes [9 and 2d, the electrode l9 representing the work to be plated. These electrodes l9 and 20 are connected through conductors 38 and 39 to the negative and the positive terminals 36 and 3'! respectively of a plating generator [6 indicated by its rotary armature A and stationary field coils or field 32. This field has a pair of terminals 42 and 43. A conductor 46 leads from field terminal 42 to a terminal 44, and a conductor 4| leads from field terminal 43 to a terminal 45, both terminals 44 and 45 being carried by a reversal switch IS. The terminal 44 connects with switch contacts 48 and 49, while terminal 45 connects with switch contacts 58 and 5 l. The switch contacts 48, 49 and 50, 5| are unitary with a movable switch member 29 diagrammatically indicated as being slidable in guides 46 and 41.

The reversal switch 16 also has two pairs of stationary contacts I2, l3 and l4, It. The switch contact 52 is connected with terminal 56 of an exciter H by way of conductor 65, point 6!, and conductor Gil. The switch contact I3 is connected with terminal 55 of the exciter l l by way of conductor 52, point 59, and conductor 58. The switch contact I4 is connected to terminal 55 of the exciter H by way of conductor 63, point 59, and conductor 58, while switch contact i5 is connected to terminal 56 of the exciter H by way of conductor 6d, point 6 l, and conductor 6! The exciter H is indicated by a rotary armature 52 with slide contacts or brushes 53 and 54 and by a field coil or field 57.

In the Fig. 1 wiring diagram the switch member 29 being subject to the pull of a spring 28 has closed contact 5| upon contact !5 and contact 49 upon contact M. In this way the exciter terminal 55 is connected to terminal 42 of the field of the plating-generator In by way of conaces-m7 ductor 58, point 59, conductor 5-3, closed switch contacts 14 and 49, switch terminal, and conductor- 4il. The exciter terminal 56 is connected to the terminal '43 of the plating generator field by way of conductor 6'0,-point 6l, conductor 64', closed switch contacts I 5 and 5|, switch terminal 45, and conductor ti. This connection between the exciter I! and the plating-generator field represents the plating phase. A field rheostat 34 is shown in conductor 4-1.

If the switch member 29 is moved to the left against the tension of spring'28 it first breaks contacts It and 49, as well as contacts i5 and 51, and then closes contact 48 upon contact 12, as well as contact 50 upon contact i3, thereby connecting the exciter terminal-55 to field terminal-43 and exciter terminal '55 to field terminal 42 of the plating-generator.

A solenoid 21 and an armature 30 unitary with the switch member 29 areprovided to effect this movement from right toleft of the switch member 29. The solenoid 27 consists of the usual core 69 encircled by a coil Hi having conductors H11 and 1! leading to stationary contacts 24 and 25 respectively, a battery'B in conductor supplying current for energizing solenoid coil 1B. The contacts 24 and 25 slide upon a rotating nonconducting disc 22 herein also termed a timing member, which carries a conducting segment or contact 23. This disc is uniformly rotated as indicated by a motor 25 and thus represents a timing member as part of a timing device 2 I.

When the conducting segment '23 closes contacts 24 and 25 it energizes solenoid 2! which attracts armature 35 and thereby shifts the switch member 29 to the Fig. 2 position, this condition being maintained as long as the segment 23 keeps the contacts 24 and 25 closed. Thus the deplating phase is maintained as long as contacts '24 and 25 are closed. Correspondingly, the plating phase is maintained as long as the contacts 24 and 25 are open. The respective and relative lengths of these phases are diagrammatically and illustratively shown in Fig. 1a with arc A1 indicating the plating phase, and are A2 indicating the deplating phase, although disregarding the distance ac between contacts 24 and 25 '(Fig. 4).

It is important for the practice of this invention to be able to control the length of time during which the switch member 29 moves from the moment of opening one set of switch contacts to the moment of closing the otherset of switch contacts, in other words,-the time during which the switch member 29 movesirom its Fig. 1 to its Fig. 2 position in reversing the field current of the plating-generator 10. Means for controlling this time interval may comprise, for example, the adjusting screw 3| for varying the tension of spring 28 by way of arm 66 swingable about point 61, to which arm the spring 28 is anchored at 68, and/or by a chang in the mass of the movable switch member 29,; and/or by variation of the strength of the'solenoid energizing battery B.

There is provided a condenser 33 connected to terminals 42 and 43, that is in parallel to the field 32 of the plating-generator III, for establishing a resonant circuit.

Fig. 3 shows in diagrammatic form the variation with time of the field current and field voltage of the plating-generator ill in the course of an operating cycle. This operating cycle consists of a plating phase' G, a deplating .phase D, and a pair of transitional phases 0 -and O" which represent the time interval during which the movable switch member 29 is in transit :and all the switch contacts are openandthe exciter-terminals 55 and 5.6 are disconnected-fromthe field terminals 42 and 4:3 of the plating-generator. The field current of the plating-generator is represented by the line i in the .Fig. .3. graph, the voltage being represented by the line v.

A single operating cycle according to 3 extends over-the length orinterval :N of the dlagram. The course of the current within that cycle visas follows:

Point K1 represents the. end, .of a depleting phase D at which theswitch member 29 begins to change from its Fig. 2 to its Fig. 1 position. The line K1K2 represents the variation of the field current 2'. during ail-initial; portion of the resonance characteristic, of a parallel resonant circuit comprising the field winding .32 as an inductance and the capacitance :33 connected in parallel therewith. This initial portion of the resonance characteristic comprises the first half cycle of a damped cosine wave, utilized by this invention for reversing the field current. The dot-and-dash line W subsequent to point K2 indicates substantially the complete damped resonance wave train of field current if it were allowed to develop. Point K2 represents the end of the transition phase 0, at whichpoint the switch member 29 reaches the Fig. 1 position.

The line K2-Ks represents the field current during the plating phase G correspondin to the connections and conditions of the Fig. .1 diagram.

Next is the line IQK4 representing the field current variation during the. transition phase 0'', that is the transition from the platingphase to the deplating phase.

Then follows the 1ine'K4fK5 representing the field current during the deplating phaseD, corresponding to the connection and conditions of the Fig. 2 diagram.

The transition phase 0 is similar to the transition phase .0 exceptthat it is in the opposite direction.

The variation of the field voltage 2; (see'Fig. 3 graph) of the plating-generator in "the-course of an operating cycle is as follows:

Beginning at point in which coincides in time with point K1 (above discussed) the voltage rises to a maximum or peak value 'Umax occurring at the instant when-currentz' passes through its zero value at point M only to drop to point on coinciding in time with point'Kzabove discussed.

The variations of the currentzand of the concurrent voltage was in the" transition phases 0 or O" are those which occur in a parallel resonant circuit under the conditionthat a direct current flowing into this circuit is suddenly in terrupted. This inventiontakes advantage .of and utilizes thesurge of voltageand current incident to such interruption.

A steady field voltage represented by line 112-903 in the Fig. 3 graph is established'for theplating phase G concurrent with thesteady field current of line K2+K3 and correspondingto the conditions of the Fig. l-diagram.

Beginning atpoint vgcoinciding in time with point K3 (above discussed) :the voltage rises again to a maximum value Umax equalito although in the opposite direction of the maximum value .of .voltage reached during the :earlier transition phase 0. "The variations. of voltageand current during the second. transition-phase 0",. that is from ointvs byway of apeakvalue. 'Dmax to point or. are :on thesame: orderzasithose occur- 7. ring during the first transition phase (above discussed) A steady voltage represented by line v4-'u5 is then established for the duration of the deplating phase D in completing the operating cycle.

0 indicates the transition into the next operating cycle marked by end points K6 and Us for the field current and the field voltage respectively. Indeed a sequence of Fig. 3 operating cycles are represented in Fig. 11 in reduced scale, with G and D designating the platingand the deplating phases respectively, and O and 0 indicating the transition phases.

' The lengths of the phases G, D, O, and O of the Fig. 3 operating cycle are established and controlled by the timing device 2| (see Figs. 1 and 2) which can be operated to repeat the cycle a desired number of times in the course of a plating operation. That is to say, the uniformly rotating timing member 01' contact bearing disc 22 of the device (its sense of rotation being indicated by arrow Q) by closing the contacts 24 and 25 closes the energizing circuit for solenoid 21 to shift the switch member 29 and then hold it in the Fig. 2 position for the duration of a deplating phase D. Continuing rotation of member 22 opens contacts 24 and 25 de-energizing the solenoid 2i and allowing the switch member 29 to assume and maintain the Fig. 1 position for the duration of a plating phase G.

Figs. 4 to show sequential rotational positions of the timing member 22 in their time relationship to the Fig. 3 graph. That is, Fig. 4 shows the timing member 22 with segment 23 at the instant of opening the contacts 24 and 25 corresponding to point K1 of the Fig. 3 graph, initiating the transition from the depiating phase D to the plating phase G.

Figs. 5, 6, and '7 show intermediate sequential positions of the timing member 22 during the interval that the contacts 24 and 25 are open, that interval being illustratively indicated by the arc A1 (see Fig. 1a) of rotation of the member 22, maintaining the plating phase. The Fig.

8 position of the member 22 represents the instant at which contacts 263 and are closed corresponding to point K3 in the Fig. 3 graph, initiating the transition from the plating phase G to the deplating phase D. The member 22 then passes through an intermediate (Fig. 9) position with the contacts 24 and 25 still closed by the conducting segment 23 maintaining the deplating phase illustratively indicated by arc A2 (see Fig. 1a) of rotation of the member 22. Thus at the end of one revolution the timing member 22 reaches the Fig. 10 position representing the instant when the contacts 24 and 25 again open to conclude the deplating phase and to initiate the transition to another plating phase.

Fig. 12 represents an enlarged detail view of that portion of the Fig. 3 graph during which the reversal switch i6 operates, that is the transition phase 0, showing the maximum value of the field current i flowing in one direction at 01, the maximum value of the current flowing in the opposite direction at point 02, and showing the current in the course of reversal passing through its zero value at 03.

Since the transition phase 0' represents the time interval during which the switch member 29 is in transit, there are shown sequential positions of the switch member in Figs. 13, 1 15 coordinated to or coincident in time with the points 01. O3, and 02 of the resonance wave portion of 8 the Fig. 12 graph. That is, in Fig. 13 at point 01 the switch member 29 is about to move from its Fig. 2 position towards the Fig. 1 position and hence is just about to break contacts 12 and 48 as well as contacts l3 and 50 at point O1the starting point of the resonance wave.

In Fig. 14 the switch member 29 is shown in transit, that is at the instant of passing through an intermediate position while all switch contacts l2 and 48, i3 and 50, I4 and 49, I5 and 5| are open.

Moving further concurrent with the resonance wave the switch member then reaches its Fig. 15 end position (corresponding to its position in the Fig. 1 diagram) Where it closes contacts [4 and 49 as well as contacts [5 and 51 substantially coincident in time with point 02 of the resonance wave of field current i.

Fig. 16 represents the wiring diagram of the field circuit including the field exciter II with a simplified showing of the connections in the reversal switch to correspond to the starting position of the switch member 29 of Fig. 13, and thus corresponding to the starting point 01 in Fig. 12 of the resonance wave of the field current 1'. These connections are represented in Fig. 16 by intersecting dotted lines, namely by the dotted line connection (Z1 between terminal 44 and point 6! (see also Fig. 2) and the dotted-line connection d2 between terminal and point 59 (see also Fig. 2).

Fig. 17 shows the wiring diagram of the field circuit in the manner of Fig. 16 although with all switch contacts open corresponding to the intermediate transitional position of the switch member 29 of Fig. 14, and thus corresponding to the zero point 03 in Fig. 12 of the resonance wave of the field current 2'. Hence no connections are shown between terminals 44, 45, and points 59, 6|.

Fig. 18 is the wiring diagram of the field circuit when the switch member 29 has reached the end position of Fig. 15 corresponding to point 02 (in Fig. 12) of the resonance wave of the field circuit 2'. Accordingly the connections now established by the switch member 29 are indicated by parallel dotted lines, namely by the dotted line connection d3 between terminal 44 and point 59 (see also Fig. 1) and the dotted line connection d4 between terminal 45 and point 5| (see also Fig. 1)

Operation Referring to Fig. 3, let it be assumed that the cycle of the plating operation starts at point K1 with the rotary timing member 22 (see Fig. 4) at a point to just about break contacts 24 and 25 herein also called the timing contacts. Prior to point K1 While these contacts were closed the switch member 29 was being held in the Fig. 2 position. due to the current from battery B energizing the solenoid 27 holding attracted the armature 39 of the switch member. Breaking of these contacts at point K1 de-energizes the solenoid and releases the switch member 29 while allowing spring 28 to return it to the Fig. 1 position. The time it takes for the switch member to be thus returned is represented by the phase or time interval 0. That is, the breaking of contacts 24 and 25 allows the switch member 29 to break contacts I2 and 48 as well as contacts 13 and 50 of the field exciter circuit and at the end of the phase 0' to close contacts [5 and as well as contacts l4 and 49 whereby the field current from exciter H through the field 32 of the plating generator H) is now established in a reverse direction at point K2.

During, the transitional phase 0., the field voltage rises from a value V1 relative to the reference line L to; a high value Vmax, then drops to a value V2. During the: same time interval the field current 2'. changes smoothly from point K1 below the reference line to point K2 above the reference line. This smooth and rapid reversal of the field current is the result of the functioning of the aforementioned resonant circuit the sequential characteristic conditions of which are shown in Figs. 12 to- 18. The transitional phase 0' of Fig. 3 shown enlarged in Fig. 12 represents the time interval during which the switch member 29 is in transit. This interval is characterized by the end points 01 and 02 of the aforementioned resonance wave. portion and by the intermediate or zero point 03. That is, at point 01 the Fig. 13 position ofthe switch member 29 is in fact that of Fig. 2,. with Fig. 16 indicating (see arrow 2'1) the direction of the field current as supplied by the exciter H.

While the switch member 29 is in transit (see Fig. 14) after breaking the contacts I3 and 59 as well as l2 and 48 at point 01 of Fig. 12, there becomes eil'ective the resonant circuit due to the inductance of the field coils 32 of plating generator Ill and the capacitance 33. That is to say, after interruption of the field exciter output current by the reversal switch, if the resonance were allowed to develop it would assume the form of a damped wave W indicated in dot-anddash line (see Fig. 3). However, according to this invention, after the resonating current has passed through its first zero value at point M (in Fig. 3) or point 03 (in Fig. 12) and about the moment it reaches its first opposite value or peak at the end of the first half wave length (Z being the full wave length), the switch member 29 reaches its Fig. l or Fig. 15 position closing the field circuit at point K2 (of Fig. 3) or point 03 (of Fig. 12) in reverse to the direction it had at point K1 (of Fig. 3) or point 01 (01 Fig. 12). That is, the switch member assumes the Fig. 1 ('or Fig. 15) closed position at point 02 (of Fig; 12) just when the resonating current has reached its full value in the direction of arrow is (see Fig. 18) which is equal and opposite to the value of the field current indicated in Fig. 16 by arrow ii at point 01. Thus begins a plating period G proper at full current value at point K2 (see Fig. 3) continuing to point K3 while the switch member 29 remains in Fig. 1 position although the timing member 22 rotates through the Figs. 5, 6, and '7 positions to the Fig. 8 position, that is a rotation corresponding to the arc A1 of Fig. 1a.. At this point K3 the timing contacts 24 and 25 are closed by the contact segment 23 of timing, member 22 (see Fig. 8) energizing the solenoid 21 which shifts the switch member 29 from the Fig. l position to the Fig. 2 position thereby again interrupting and reversing the field current 2'. While the switch member 29 is in transit during phase 0' (see Fig. 3), the field current i reverses along the line Kz K4 in a manner and under conditions similar to those described for the earlier phase 0 between points K1 and K2 of Fig. 3. Thus at K4 there starts the depla-ting phase D proper, the current being reversed from its full value at K: to its full opposite value at K4. The deplating period D continues to point K concluding a complete operating cycle N. One full revolution of the timing member 22 thus produces a complete operating cycle. Rotation of the timing member may be continued to produce a sequence of any desired number of cycles. Several repetitions of. that cycle may be required or desired for a plating operation, such a sequence being indicated in the reduced-scale diagram of Fig. 11.

It will be understood that while the field current i reverses from K3 to K4 (Fig. 3) the field voltage changes from a value V3 by way of peak from; to a value V4 equal and opposite to the value V3. It will also be understood in view of the relationship between Fig. 3 and Fig. 12 that the points K1 and K2 of phase 0 in Fig. 3 correspond to points 01 and Oz of phase 0 of Fig. 12. One factor necessary to establish the operating cycle or cycles according to this invention and in accordance with graphs of Figs. 3 and 11 is that the capacity of the condenser or capacitance 33 should be large enough to keep the peak field voltage Vmax within safe limits to prevent damage to the field coils or the condenser. A second factor is with respect to the operation of the reversal switch I 6, in that the length of the time interval during which the switch member 29 is in transit in either direction, as represented by phases 0 and 0", must be coordinated to the resonance or wave characteristic of the resonant circuit. By suitable adjustments the time of transit of the switch member 29, that is its pull-up time as well as its release time, is made to coincide with the-first half cycle or half wave length of the resonance that develops between the inductance of generator field windings 32 and the capacitance 33. That is, the switch member 29 should disconnect the field exciter H from the field windings 32 at a predetermined instant and then reconnect the field exciter H in reverse polarity to the. field 32 substantially at the time that a subsequent resonant peak of opposite current value occurs incident to the field current 2' having reversed itself of its own accord during the time interval 01 to 02 (Fig. 12) during which interval the field remained disconnected from its exciter while the switch member 29 was in transit. While in Figs. 3 and 11 the closing of the reverse contacts takes place at the first peak, it need not of necessity be so limited inasmuch as the timing of the switch member might be such that the reverse closing takes place at a following peak of the resonance wave, for example at K2.

The size or capacity of the condenser 33 in the resonant circuit may be arrived at from the machine constants of the plating generator l0, namely the inductance of the field windings 32 of the plating generator; the maximum safe peak voltage across the field windings 32, and the magnitude of the field current i.

For a given set of these machine constants, the relationship is that the larger the condenser 33 is chosen the lower will be the peak voltage (Vmax in Fig. 3) across the field incident to the reversal of field current 2 during the open phase of the reversal switch l6, and the larger will be the time interval required during which the reversal of the field current 2' is to take place coinciding with the first half period (K1K2) of the resonant wave. Therefore, in the practice of this invention the capacitance 33 is chosen large enough to limit the resulting peak field voltage Vmax to a predetermined safe value, which in turn fixes the duration of the first half cycle of the resonant current wave to which in turn the timing of the switch member 29 must be adjusted. That is, having determined the duration of the first half cycle of the resonant wave, the required characteristics of the reversal switch I5 are that II the time required for a reversal movement of the switch member 29 should coincide or be in tune with the first half cycle (K1-K2) in Fig. 3, or

O1-O2 in Fig. 12 of the resonant wave of the field current 2'.

What we claim is:

1. Apparatus for electroplating in which a plating generator provides an output of direct current for passing through a plating bath, and has an auxiliary power source plOVidlng field excit ing current for said generator, characterized by switch means for reversing the direction of said field-excitin current to effect reversal of the generator output current from a plating phase to a shorter deplating phase, a capacitance connected in parallel with the generator field to constitute with said field a parallel resonant circuit adapted to discharge the stored energy of said field in the form of a resonant current wave when the fieldexciting current is interrupted by said switch means, and timing means operatively associated with the switch means so as to establish timedrelationship between the operation of the switch means and the time period of said resonance wave in such a manner that said switch means re-establishes the field current in reverse direction substantially at a time when the resonance current wave substantially reaches a peak of correspondingly reversed current value.

2. Apparatus according to claim 1, with the addition of actuatin means for operating said reversing switch means along with said timing means to establish at least one predetermined operating cycle having a sequence of operating phases each of predetermined lengths of time, which cycle comprises closing the field-excitin circuit to initiate a plating phase during which the field-exciting current fiows in a direction to effect plating, opening the field circuit to terminate the plating phase while initiating a transition phase as well as initiating said resonant discharge of the field energy while rendering said timing means effective, re-establishing the fieldexciting current in reverse at the end of the transition phase while initiating a deplatin phase, and interrupting the reverse field current to terminate the deplating phase.

3. Apparatus for electroplating in which a plating generator provides direct current for passing through a plating bath, and has a pair of field terminals connectible to an auxiliary source of current having a pair of exciter output terminals connectible to said field terminals for supplying current thereto, characterized by switch means for reversing the direction of the field exciting current by reversing the connection between said field terminals and said eXciter output terminals to efiect reversal of the generator output current from a plating phase to a shorter deplating phase, said switch means comprising a double-pole double-throw switch member operable for reversing said connections, a capacitance connected in parallel with the generator field to constitute with said field a parallel resonant circuit adapted to discharge the stored energy of the field in the form of a resonant current wave when the field-exciting current is interrupted by said switch member, and timing means operatively associated with said switch means so as to establish timed relationship between the operation of the switch member and the time period of said resonance wave in such a manner that said switch means re-establishes the field current in reverse direction substantially at a time when the resonance current wave reaches a peak of correspondingly reversed current value.

4. Apparatus according to claim 3, with the addition of actuatin means for operating said reversing switch member along with said timing means to establish a predetermined operating cycle having a sequence of operating phases each of predetermined length of time, which comprises closing the field exciting circuit to initiate a plating phase during which the field-exciting current flows in a direction to effect plating, opening the field circuit to terminate the plating phase while initiating a transition phase as well as initiating said resonant discharge of the field energy while rendering said timing means effective, re-establishing the field-exciting current in reverse at the end of the transition phase while initiating a deplating phase, and interrupting the reverse field current to terminate the deplating phase.

5. Apparatus for electroplating in which a plating generator provides an output of direct current for passing through a plating bath, and has an auxiliary power source providing field exciting current for said generator, characterized by switch means for reversin the direction of said field exciting current to effect reversal of the generator output current from a plating phase to a shorter deplating phase, capacitance connected in circuit with the generator field to constitute with said field a resonant circuit adapted to discharge stored energy of the field in the form of a resonant wave when the field exciting current is interrupted, and timing means operatively associated with the switch means so as to establish timed relationship between the operation of the switch means and the time period of said resonance wave in such a manner that said switch means re-establishes the field current in reverse direction when the resonant current represented by said wave has attained a value which encourages the re-establishment of the field exciting current in said reverse direction.

6. Apparatus according to claim 5, in which the timing means comprise adjusting means whereby the field exciting current is re-established in said reverse direction when the resonant current has attained said reverse direction.

'7. Apparatus according to claim 5', characterized by the fact that capacitance is connected in parallel with said generator field to constitute a parallel resonant circuit.

RICHARD SHO'ITENFELD. HANS KUEHL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,956,411 Bonine Apr. 24, 1934 2,451,341 Jernstedt Oct. 12, 1948 

